Nuclear magnetic resonance (NMR) spectroscopy is capable of non-invasive online determinations of intracellular concentrations and turnover of numerous metabolites as well as inorganic ions. We have been applying this technique to the study of cellular physoilogy both in vitro and in vivo. Studies have been performed on the effect hypoxia and hypovolemic shock on the relative concentrations of high energy phosphates in the in vivo rat brain and kidney. The 14N resonances from the in vivo rate kidney, brain, liver and leg rat have also been characterized. In addition, we have made progress in combining NMR with tissue culture preparations, in order to use the advantages of a well defined and controlled cell population to investigate cellular physiology using this powerful technique